strtod(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

STRTOD(3)               Linux Programmer's Manual              STRTOD(3)

NAME         top

       strtod, strtof, strtold - convert ASCII string to floating-point
       number

SYNOPSIS         top

       #include <stdlib.h>

       double strtod(const char *restrict nptr, char **restrict endptr);
       float strtof(const char *restrict nptr, char **restrict endptr);
       long double strtold(const char *restrict nptr, char **restrict endptr);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       strtof(), strtold():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION         top

       The strtod(), strtof(), and strtold() functions convert the
       initial portion of the string pointed to by nptr to double,
       float, and long double representation, respectively.

       The expected form of the (initial portion of the) string is
       optional leading white space as recognized by isspace(3), an
       optional plus ('+') or minus sign ('-') and then either (i) a
       decimal number, or (ii) a hexadecimal number, or (iii) an
       infinity, or (iv) a NAN (not-a-number).

       A decimal number consists of a nonempty sequence of decimal
       digits possibly containing a radix character (decimal point,
       locale-dependent, usually '.'), optionally followed by a decimal
       exponent.  A decimal exponent consists of an 'E' or 'e', followed
       by an optional plus or minus sign, followed by a nonempty
       sequence of decimal digits, and indicates multiplication by a
       power of 10.

       A hexadecimal number consists of a "0x" or "0X" followed by a
       nonempty sequence of hexadecimal digits possibly containing a
       radix character, optionally followed by a binary exponent.  A
       binary exponent consists of a 'P' or 'p', followed by an optional
       plus or minus sign, followed by a nonempty sequence of decimal
       digits, and indicates multiplication by a power of 2.  At least
       one of radix character and binary exponent must be present.

       An infinity is either "INF" or "INFINITY", disregarding case.

       A NAN is "NAN" (disregarding case) optionally followed by a
       string, (n-char-sequence), where n-char-sequence specifies in an
       implementation-dependent way the type of NAN (see NOTES).

RETURN VALUE         top

       These functions return the converted value, if any.

       If endptr is not NULL, a pointer to the character after the last
       character used in the conversion is stored in the location
       referenced by endptr.

       If no conversion is performed, zero is returned and (unless
       endptr is null) the value of nptr is stored in the location
       referenced by endptr.

       If the correct value would cause overflow, plus or minus
       HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
       return type and sign of the value), and ERANGE is stored in
       errno.

       If the correct value would cause underflow, a value with
       magnitude no larger than DBL_MIN, FLT_MIN, or LDBL_MIN is
       returned and ERANGE is stored in errno.

ERRORS         top

       ERANGE Overflow or underflow occurred.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────────────────────────┬───────────────┬────────────────┐
       │Interface                      Attribute     Value          │
       ├───────────────────────────────┼───────────────┼────────────────┤
       │strtod(), strtof(), strtold()  │ Thread safety │ MT-Safe locale │
       └───────────────────────────────┴───────────────┴────────────────┘

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, C99.

       strtod() was also described in C89.

NOTES         top

       Since 0 can legitimately be returned on both success and failure,
       the calling program should set errno to 0 before the call, and
       then determine if an error occurred by checking whether errno has
       a nonzero value after the call.

       In the glibc implementation, the n-char-sequence that optionally
       follows "NAN" is interpreted as an integer number (with an
       optional '0' or '0x' prefix to select base 8 or 16) that is to be
       placed in the mantissa component of the returned value.

EXAMPLES         top

       See the example on the strtol(3) manual page; the use of the
       functions described in this manual page is similar.

SEE ALSO         top

       atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strfromd(3),
       strtol(3), strtoul(3)

COLOPHON         top

       This page is part of release 5.11 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22                      STRTOD(3)

Pages that refer to this page: gawk(1)pcpintro(1)pmstore(1)strace(1)atof(3)atoi(3)nan(3)scanf(3)strfromd(3)strtol(3)strtoul(3)locale(7)